Various electronic devices, such as semiconductor devices, and photonic devices, such as lasers and solar devices, include or may desirably include silicon germanium tin (SixGe1-xSny) layers. For example, SixGe1-xSny layers can be used to form direct band gap devices, quantum well structures, and/or may be used to provide strain in, for example, an adjacent germanium layer to increase carrier mobility in the germanium layer. SixGe1-xSny layers can also be used to form tunable band gap devices as well as optical devices having tunable optical properties. To obtain the desired device properties, the SixGe1-xSny layers generally have a crystalline structure, which generally follows the crystalline structure of an underlying layer, such as a buffer layer.
SixGe1-xSny layers can be deposited or grown using a variety of techniques. For example, vacuum processes, including molecular beam epitaxy and ultra-high vacuum chemical vapor deposition, have been used to form SixGe1-xSny films. Unfortunately, such techniques are slow, expensive, and thus generally not well suited for high-volume manufacturing.
The germanium precursor for such processes typically includes digermane (Ge2H6) or trigermane (Ge3H8). When the film includes silicon, the silicon precursor typically includes a disilane (Si2H6), trisilane (Si3H8), or other higher order silane compounds, or hetero-nuclear Si—Ge compounds with the general formula of (H3Ge)xSiH4-x (x=1-4), (H3Si)xGeH4-x (x=1-4).
Although such processes generally work to deposit or grow crystalline SixGe1-xSny layers, use of digermane, trigermane, or higher order germane precursors and/or disilane or trisilane, is problematic in several respects. For example, formation of films or layers including SixGe1-xSny using digermane or higher order germane precursors, such as trigermane, is not selective when certain carrier gasses (e.g., hydrogen) and/or dopants (e.g., p-type dopants) are used with the precursor. Also, digermane is relatively unstable (explosive) in concentrated form; as a result, an amount of the precursor contained in a vessel may be limited, typically to less than 154 grams, which, in turn, causes throughput of processes using such a precursor to be relatively low. In addition, digermane and higher order germanes are relatively expensive. Similarly, higher order silanes are relatively expensive and can result in relatively slow growth rates. Accordingly, improved processes for forming SixGe1-xSny are desired. Further, improved methods suitable for high-volume manufacturing of structures and devices including a layer of SixGe1-xSny are desired.